Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
  • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
  • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
  • H01L29/76—Unipolar devices, e.g. field effect transistors
  • H01L29/772—Field effect transistors
  • H01L29/78—Field effect transistors with field effect produced by an insulated gate
  • H01L29/786—Thin film transistors, i.e. transistors with a channel being at least partly a thin film
  • H01L29/7869—Thin film transistors, i.e. transistors with a channel being at least partly a thin film having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
  • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
  • H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
  • H01L29/49—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET
  • H01L29/4908—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET for thin film semiconductor, e.g. gate of TFT
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
  • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
  • H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
  • H01L29/49—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET
  • H01L29/51—Insulating materials associated therewith
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
  • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
  • H01L29/66007—Multistep manufacturing processes
  • H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
  • H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
  • H01L29/66409—Unipolar field-effect transistors
  • H01L29/66477—Unipolar field-effect transistors with an insulated gate, i.e. MISFET
  • H01L29/66742—Thin film unipolar transistors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
  • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
  • H01L29/66007—Multistep manufacturing processes
  • H01L29/66969—Multistep manufacturing processes of devices having semiconductor bodies not comprising group 14 or group 13/15 materials
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
  • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
  • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
  • H01L29/76—Unipolar devices, e.g. field effect transistors
  • H01L29/772—Field effect transistors
  • H01L29/78—Field effect transistors with field effect produced by an insulated gate
  • H01L29/786—Thin film transistors, i.e. transistors with a channel being at least partly a thin film
  • H01L29/78696—Thin film transistors, i.e. transistors with a channel being at least partly a thin film characterised by the structure of the channel, e.g. multichannel, transverse or longitudinal shape, length or width, doping structure, or the overlap or alignment between the channel and the gate, the source or the drain, or the contacting structure of the channel

Definitions

• the present invention is related to systems and methods useful in fabricating thin film structures.
• Metal oxide semiconductors such as zinc oxide (ZnO) and indium gallium zinc oxide (InGaZnO) are attractive for device fabrication due to their high carrier mobility, low processing temperatures, and optical transparency.
• Thin film transistors (TFTs) made from metal oxide semiconductors are particularly useful in active-matrix addressing schemes for optical displays.
• the low processing temperature of metal oxide semiconductors allows the formation of display backplanes on inexpensive plastic substrates such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN).
• PET polyethylene terephthalate
• PEN polyethylene naphthalate
• the transparency of oxide semiconductor TFTs leads to improved pixel apertures and brighter displays.
• amorphous silicon (a-Si) TFTs reduce pixel aperture because a-Si devices are light sensitive and must be shielded from the light.
• metal oxide semiconductor TFTs have great potential due to their transparency and the potential for high performance devices formed at or near room temperatures, fabrication of stable devices remains a challenge.
• Metal oxide semiconductor TFTs may exhibit hysteresis in their characteristics as a function of gate- bias. Development of metal oxide semiconductor technology is ongoing, and current efforts are focused on reducing or eliminating hysteresis to enhance TFT stability. The present invention fulfils these and other needs, and offers other advantages over the prior art.
• Embodiments of the invention are directed to thin film electronic structures and methods for fabricating the thin film structures.
• One embodiment of the invention involves a method of fabricating a multilayer semiconductor structure.
• An electrode layer e.g., a gate electrode
• a dielectric layer is formed proximate to the electrode layer.
• the dielectric layer is exposed to a hydrogen-containing plasma.
• a metal oxide semiconductor layer is formed proximate to the dielectric layer.
• Another embodiment of the invention involves a method for making a metal oxide semiconductor device. The process involves forming an electrode layer and forming a dielectric layer on the electrode layer.
• the dielectric layer is processed to create a non-uniform hydrogen profile in a hydrogenated region at the surface of the dielectric layer.
• the concentration of hydrogen in the hydrogenated region is relatively high at the surface of the dielectric and the hydrogen concentration in the hydrogenated region decreases within the bulk of the dielectric layer.
• a semiconductor layer comprising a metal oxide semiconductor is formed over the dielectric layer.
• the multilayer semiconductor structure includes an electrode and a dielectric layer disposed proximate to the electrode.
• the multilayer semiconductor structure also includes a semiconductor layer comprising a metal oxide semiconductor formed proximate to the dielectric.
• a hydrogenated region is formed at a semiconductor-dielectric interface of the dielectric layer. The hydrogen concentration of the hydrogenated layer is relatively high at the semiconductor-dielectric interface and the hydrogen concentration decreases in concentration from the semiconductor-dielectric interface into one or both of the dielectric layer and the semiconductor layer.
• Figure 1 is a flow diagram illustrating a process for fabricating metal oxide semiconductor thin film transistors using plasma exposure in accordance with embodiments of the invention
• Figure 2 is a cross section of a device including a plasma hydrogenated region in accordance with embodiments of the invention
• Figures 3A-3D are secondary ion mass spectroscopy (SIMS) plots for four ZnO- Al 2 O 3 sample structures exposed to deuterium (D 2 ) plasma for various lengths of time in accordance with embodiments of the invention;
• Figure 4 shows current- voltage plots (forward and reverse sweeps) for the samples of Figures 3A-3D which demonstrate the improvement of the threshold voltage, stability with increasing D 2 plasma exposure;
• Figure 5 shows current- voltage plots (forward and reverse sweeps) for a TFT having an anodized Al 2 O 3 dielectric which demonstrate the improvement in stability and performance obtained by hydrogen plasma exposure in accordance with embodiments of the invention.
• Figure 6 shows current-voltage plots (forward and reverse sweeps) for a TFT having an anodized Al 2 O 3 dielectric with a sputtered SiO 2 layer which demonstrate the improvement in stability and performance obtained by hydrogen plasma exposure in accordance with embodiments of the invention.
• Metal oxide semiconductors such as zinc oxide (ZnO) and related alloys such as indium gallium zinc oxide (InGaZnO), have recently generated great interest as the active layer of transparent thin film transistors (TFTs).
• This group of semiconductors can be processed at room temperature to create flexible circuits including transparent transistors which have high carrier mobility, making them potentially ideal for many display applications.
• TFTs transparent thin film transistors
• This group of semiconductors can be processed at room temperature to create flexible circuits including transparent transistors which have high carrier mobility, making them potentially ideal for many display applications.
• techniques to enhance the stability of the devices are needed.
• Metal oxide semiconductor TFTs may exhibit instability in their current-voltage transfer characteristics and threshold voltage V T due to a gate-bias induced hysteresis. Approaches described herein mitigate this hysteresis and also improve overall TFT operation.
• Embodiments of the invention are directed to methods for enhancing the stability of metal oxide semiconductor TFTs by exposure of the gate dielectric to a hydrogen- containing plasma.
• the methods described are cost effective and relatively easy to control, and are particularly advantageous for roll-to-roll fabrication.
• the approaches discussed herein involve exposure of at least the dielectric layer of the TFT to a hydrogen- containing plasma prior to deposition of the metal oxide semiconductor, e.g., ZnO, InGaZnO, InZnO, ZnSnO, and/or other metal oxide semiconductors.
• Plasma exposure of the dielectric creates a plasma hydrogenated region at least within the dielectric layer at the semiconductor-dielectric interface and may extend into the dielectric layer and/or the semiconductor layer.
• the plasma hydrogenated region significantly stabilizes the gate- bias transfer characteristics and the threshold voltage shift of the devices and also improves carrier mobility, thereby enhancing overall TFT performance.
• Hydrogenation of silicon nitride gate dielectrics during plasma enhanced chemical vapor deposition has been shown to increase carrier mobility in metal oxide semiconductor TFTs over similar TFTs formed using non-PECVD gate dielectrics, or PECVD gate dielectrics containing reduced levels of hydrogen.
• the increase in carrier mobility in the TFTs with PECVD SiN dielectrics containing increased levels of hydrogen may be attributed to defect passivation in the channel as the high concentration of hydrogen in the dielectric diffuses into the semiconductor.
• Hydrogenation of the gate dielectric during formation via PECVD differs in both process and resulting structure from hydrogen-containing plasma exposure after dielectric formation.
• FIG. 1 is a flow diagram illustrating fabrication of one configuration of a metal oxide semiconductor TFT in accordance with embodiments of the invention.
• the TFT gate electrode is formed 110 on a substrate.
• the substrate may be a rigid or flexible, transparent or opaque material, such as glass, metal or plastic.
• Low cost flexible substrates allow fabrication by roll to roll processing which generally reduces manufacturing costs.
• Low cost flexible substrates may comprise a polymer material such as PEN or PET.
• Polymers are desirable for display applications because of their optical transparency. These substrate materials are sensitive to temperature making low temperature processing desirable.
• Metal foil is also a suitable flexible substrate for some applications.
• the gate electrode can be made of any electrically conductive material, with aluminum (Al) magnesium (Mg), tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten (W), and chromium (Cr) being of particular interest.
• the gate electrode may comprise a metal alloy, a conductive metal oxide, or a doped semiconductor.
• Aluminum (Al) and aluminum-based alloys are frequently used for circuit metallization because these materials are relatively inexpensive, can be deposited by a number known deposition processes, and are well suited to thin film applications. Suitable gate electrode deposition/patterning techniques include traditional photolithography, metal evaporation through a shadow mask, and/or other techniques known in the art.
• a dielectric layer is formed 120 on the gate electrode, such as by anodizing the gate material and/or by depositing a dielectric layer over the gate.
• a dielectric layer For example, in one implementation, aluminum is used to form the gate electrode which is then anodized to form an AI 2 O3 layer which serves as the dielectric layer for the transistor.
• the dielectric layer may include a number of sublayers. For example, a sputtered Si ⁇ 2 layer (or other dielectric) may be deposited on an anodized AI 2 O3 layer to form the gate dielectric.
• the gate dielectric is exposed 130 to a plasma containing hydrogen gas.
• the plasma includes a gas containing hydrogen and argon with a hydrogen content of at least about 5%.
• the plasma may include deuterium.
• plasma exposure involves a 5% hydrogen/95% argon gas applied at a power density of at least about 0.01 Watts/cm 2 for at least about 3-5 minutes.
• Exposure of the gate dielectric to the hydrogen-containing plasma leads to the formation 140 of a hydrogenated region at and/or near the surface of the dielectric.
• hydrogen is concentrated at the dielectric surface and the concentration of hydrogen decreases from the surface of the dielectric layer into the bulk of the dielectric layer.
• the hydrogen concentration decreases from a first level at the surface of the dielectric layer to a second, lower, level within the bulk of the dielectric layer.
• the metal oxide semiconductor is deposited 150 over the dielectric layer and the drain and source electrodes are formed 160.
• the TFT fabrication steps 110-160 may proceed at a temperature of less than about 100 C, and may be carried out at room temperature.
• FIG. 1 is a cross sectional view of a multilayer TFT fabricated by the process described above.
• the device depicted in Figure 2 represents a particular arrangement of the component layers of the TFT.
• the TFT may be built up with the drain and source electrodes initially deposited on the substrate with the semiconductor, dielectric, and gate layers arranged thereon to form a TFT. All variations of TFT configurations that allow formation of a hydrogenated region of the gate dielectric as described herein are contemplated as being within the scope of the present invention.
• the device 200 is formed on a substrate 210 that is typically insulative and may be transparent and/or flexible as previously discussed.
• a gate conductor (i.e., gate electrode) 220 is disposed on the substrate 210.
• a dielectric layer 230 is disposed on the gate conductor 220 and a metal oxide semiconductor layer 240 is disposed on the dielectric layer 230.
• Drain and source electrodes 250 are arranged on the metal oxide semiconductor layer 240.
• a plasma hydrogenated region 260 is formed at and/or near the interface of the dielectric 230 and semiconductor 240 layers.
• the plasma hydrogenated region 260 includes a region of hydrogen concentrated at the interface which may extend into one or both of the dielectric layer 230 and the metal oxide semiconductor 240 layer.
• the hydrogen extends into the bulk dielectric or semiconductor, one or both of the dielectric layer 230 and the semiconductor layer 240 exhibit a non-uniform hydrogen concentration profile.
• the hydrogen content is non-uniform, decreasing from a relatively high concentration at the dielectric-semiconductor interface 270 with decreasing concentration into the bulk dielectric 230.
• a similar non-uniform hydrogen concentration profile may be found within the metal oxide semiconductor, wherein the hydrogen concentration decreases from the interface into the bulk semiconductor
• Figures 3A -3D are secondary ion mass spectroscopy (SIMS) plots for ZnO-Al 2 O 3 structures exposed to deuterium (D 2 ) plasma for various lengths of time after the formation of the AI 2 O 3 layer and prior to the deposition of the ZnO layer.
• Graph 3 A depicts a TFT control sample (Sample A) that is not exposed to the deuterium plasma.
• the ZnO concentration 310 is substantially constant through the ZnO semiconductor region, and decreases at the ZnO-Al 2 O 3 interface 312.
• the AI 2 O3 graph 315 illustrates that the AI 2 O3 concentration increases at the ZnO-Al 2 O 3 interface and is substantially constant in the bulk of the Al 2 O 3 .
• the sample depicted in Figure 3 A was not exposed to deuterium plasma, and as a result, the D 2 concentration remains flat in the ZnO and Al 2 O 3 regions.
• FIGS 3B, 3C and 3D illustrate three ZnO-Al 2 O 3 sample TFT structures (Samples B, C, and D) with Al 2 O 3 layer exposure to 5% D 2 /Ar plasma at 500 W for 2 minutes, 5 minutes, and 10 minutes respectively.
• the D 2 concentration illustrated by graphs 327, 337 and 347, respectively, rises at the ZnO-Al 2 O 3 interface 312 and decreases into the bulk of the Al 2 O 3
• the hydrogen concentration profiles become broader with time of deuterium plasma exposure as illustrated by the graphs 327, 337, and 347.
• Figure 4 shows overlay graphs of the current- voltage transfer characteristics for Samples A, B, C, and D which illustrate the improvement of the threshold voltage stability with increasing D 2 plasma exposure.
• Graphs 410 and 411 are the forward and reverse voltage sweeps, respectively, for Sample A (no plasma exposure); Graphs 420 and 421 are the forward and reverse voltage sweeps, respectively, for Sample B (2 minute D 2 plasma exposure); Graphs 430 and 431 are the forward and reverse voltage sweeps, respectively, for Sample C (5 minute D 2 plasma exposure); and Graphs 440 and 441 are the forward and reverse voltage sweeps, respectively, for Sample D (IO minute plasma exposure).
• the instability in the Sample A is manifested as an undesirable positive shift in the threshold voltage between the forward and reverse gate voltage sweeps.
• the stability of the samples increased with D 2 exposure. Note the minimal hysteresis between the forward 440 and reverse 441 traces for Sample D which was exposed to D 2 plasma for 10 minutes.
• the carrier mobility for the D 2 plasma exposed TFTs were also increased over the carrier mobility of the TFT that was not exposed to the D 2 plasma.
• the gate metal was anodized to the desired thickness of the Al 2 O 3 , typically about 100 nm (75V).
• the device was exposed to a forming gas plasma Of Ar-H 2 composed of 95% argon and 5% hydrogen.
• the plasma exposure was performed at 500 W, typically for about 3-5 minutes.
• the sample was placed on a grounded electrode platen during the plasma exposure.
• the frequency of the plasma system is about 4OkHz.
• ZnO deposition was performed. Standard processing was then used to complete fabrication of the sample.
• Figure 5 shows current-voltage transfer characteristics demonstrating the improvement in stability and performance obtained by the hydrogen plasma treatment.
• the plot shows the current- voltage plots of two TFTs made with 520, 525 and without 510, 515 the Ar-H 2 plasma treatment described above. Note the large hysteresis between the forward 510 and reverse 515 current traces for the TFT with no plasma treatment. This instability is manifested as an undesirable positive shift in the threshold voltage.
• the second set of current traces 520, 525 is from an otherwise identical TFT on the same substrate except that the second TFT was exposed to the Ar-H 2 plasma according to the process described herein. Note the minimal hysteresis between the forward 520 and reverse 525 traces for the plasma exposed TFT. The carrier mobility for the hydrogen plasma exposed TFT was also increased over that of the TFT that was not exposed to the hydrogen plasma.
• the gate metal was anodized to the desired thickness of the AI 2 O3, typically about 100 nm (75 V). After anodization, about a 20nm thick layer of SiO 2 was RF-sputter deposited on top of the surface of the anodized AI 2 O3 layer. After deposition of the SiO 2 layer, the device was exposed to a forming gas plasma Of Ar-H 2 composed of 95% argon and 5% hydrogen. The plasma exposure was performed at 500 W, typically for about 3-5 minutes. The sample was placed on a grounded electrode platen during the plasma exposure. The frequency of the plasma system is about 4OkHz. After the plasma exposure, ZnO deposition was performed. Standard processing was then used to complete fabrication of the sample.
• Figure 6 shows current-voltage transfer characteristics demonstrating the improvement in stability and performance obtained by the hydrogen plasma treatment.
• the plot shows the current- voltage plots of two TFTs made with 620, 625 and without
• the second set of current traces 620, 625 is from an otherwise identical TFT on the same substrate except that the second TFT was exposed to the Ar-H 2 plasma according to the process described herein. Note the minimal hysteresis between the forward 620 and reverse 625 traces for the plasma exposed TFT. The carrier mobility for the hydrogen plasma exposed TFT was also increased over that of the TFT that was not exposed to the hydrogen plasma.

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• 2009
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